1. Field of the Invention
The present invention relates to coating compositions and it has particular relation to coating compositions which render surfaces such as glass chemically reactive with organic compounds and polymers. More particularly, the invention relates to coating compositions which are applied to glass fibers during their forming into a strand which is to be used as a reinforcement for resinous and elastomeric products. These compositions have come to be known in the glass fiber art as "coupling agents".
The invention is described in particular relation to the manufacture and use of glass fibers; however, the invention is applicable to the coating of any material which normally has a highly polar surface, such as an oxide-containing or hydroxyl-containing surface. The hydroxyl groups may be part of the chemical composition of the material or they may be present as bound hydroxyl groups which are normally present on the surface of glass or siliceous articles.
2. Description of the Prior Art
A glass fiber strand is composed of a multitude of fine glass filaments which are formed by being drawn at a high rate of speed from molten cones of glass located at the tips of small orifices in a bushing such as shown in U.S. Pat. No. 2,133,238. During formation, the filaments are coated while moving at a speed in excess of 5,000 up to 20,000 feet per minute with a size which contains a binder to give the strand integrity for workability for any standard textile or reinforcement use. If the strand does not have proper integrity, fuzzing occurs during these operations and eventually the strand breaks. The size also contains a lubricant for the filaments to prevent destruction of the strand by abrasion of the individual filaments against each other or against fiber handling equipment.
It is common practice to use glass fiber strands and glass fiber cloth as a reinforcement for resins. For such use, the glass fibers are coated with a coupling agent or finish material which makes the surface of the glass fibers substantive and compatible with the particular resins with which they are to be employed. These coupling agents greatly increase the dry and wet physical strengths of the glass fiber resin laminate.
When the glass fibers are used in the form of strand, i.e., roving or chopped strand or twisted strand, for resin reinforcement, the coupling agent is usually combined with the size and applied with the size to the fibers during their formation. The size employed is usually an aqueous dispersion of a film forming, synthetic binder, and a glass fiber lubricant.
Coupling agents which have been used in aqueous size compositions in the prior art include silane and siloxane materials. For example, hydrolyzable vinyl, allyl, beta chloropropyl, phenyl, thio-alkyl, thio-alkaryl, amino-alkyl, methacrylato, epoxy and mercapto silanes, their hydrolysis products and polymers of the hydrolysis products and mixtures of any of these are suitable for such use. Some of the silanes are disclosed in U.S. Pat. Nos. 2,563,288; 2,688,006; 2,688,007; 2,723,211; 2,742,378; 2,754,237; 2,776,910; 2,799,598; 2,832,754; 2,930,809; 2,946,701; 2,952,576; 2,974,062; 3,044,982; 3,045,036; 3,169,884; 3,207,623 and 3,211,684.
Another class of coupling agents which has been found to be useful are the basic (hydroxy containing) metal salts of a strong mineral acid, such as, for example, a basic chromium chloride, basic chromium sulfate, etc. These compounds are ones having a trivalent metal ion selected from the group consisting of chromium, cobalt, nickel, copper and lead, at least one hydroxyl group attached to the metal, and at least one anion of a strong mineral acid attached to the metal (as well as coordinate complexes of these compounds and mixtures thereof).
Another type of coupling agent which has been used is a complex compound of the Werner type in which a trivalent nuclear atom, such as chromium, is coordinated with an organic acid such as methacrylic acid, i.e., a methacrylic acid complex of chromic chloride. Such agents are described in U.S. Pat. No. 2,611,718. Other Werner type coupling agents having vinyl, alkyl, amino, epoxy, mercapto, thio-alkyl, thio-alkaryl, and phenyl groups are suitable for use.
Mixtures of two or more of any of these coupling agents have been used.
Roving is formed by combining a number of strands in parallel form and winding the strands on a tubular support in a manner such that the combined strands may be unwound and used to form woven roving or chopped strands. Twisted strand (singe end on a bobbin) is made according to conventional textile twisting techniques by removing the strand from the forming package and winding it on a twister bobbin. It is therefore necessary that the strand have good integrity and resistance to fuzzing during the steps employed to make the twisted strand or roving and fabricate them into forms suitable for use as a resin reinforcement.
It is desired that a treatment be provided for glass fiber strand which will render the strand capable of providing increased strength to glass fiber reinforced resinous and elastomeric products. For example, it is desired that a strand be provided which is equally useful as a reinforcement for styrenated polyester resins, epoxy resins, thermoplastic resins, natural rubber and synthetic rubbery polymers. In this regard it is desired to produce a strand which is composed of a plurality of smaller or fine strands which are easily wet-out with resin or coated or impregnated with a rubber adhesive coating.
It is an object of this invention to provide an elastomer (rubber) coated glass fiber strand, yarn, roving or textile fabric for reinforcement of elastomers (rubber). The elastomer (rubber) coated glass fiber reinforcement should adhere well to the elastomer matrix at high and low temperatures and should have long life and good strength under severe flexing conditions.
The term "elastomer" as used herein and in the claims is intended to include elastic substances such as natural latex from the Hevea tree and synthetic rubber and rubber-like materials. It also includes natural and synthetic rubber and rubber-like materials which have been chemically modified such as by chlorination to improve their physical properties. Synthetic rubber includes rubber-like materials such as chloroprene, butadiene, isoprene and copolymers thereof with acrylonitrile, styrene and isobutylene. The term "elastomer" includes natural and synthetic rubber in the uncured or unvulcanized state as well as in the cured or vulcanized state.